Renal oncocytoma mimicking hemorrhagic renal cyst

A case of oncocytoma, the radiological findings of which resembled a hemorrhagic renal cyst, is reported. Cyst fluid analysis demonstrated extremely high levels of carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA19-9). Preoperatively the lesion was regarded a malignant cyst, and radical nephrectomy was performed. Pathological diagnosis was renal oncocytoma with cystic degeneration. Although cystic change occasionally has been mentioned in oncocytoma, a high level of CEA and CA 19-9 in the cyst fluid of the cystic oncocytoma have not been reported. We discuss the variant forms of oncocytoma and tumor markers in the cyst fluid.